Thermal Considerations of Space Solar Power Concepts with 3.5 GW RF Output

11 Pages·2000·0.73 MB·English

by  Choi, Michael K

AIAA-2000-2904
THERMAL CONSIDERATIONS OF SPACE SOLAR POWER CONCEPTS WITH 3.5 GW RF OUTPUT
Michael K. Choi"
NASA Goddard Space Flight Center
Greenbelt, MD 20771
ABSTRACT
This paper presents the thermal challenge of the times as much solar radiation as that on the ground. 2
Space Solar Power (SSP) design concepts with a 3.5 Solar radiation is available in the GEO orbit
GW radio-frequency (RF) output. High efficiency almost all around the equinoxes when the satellite is
klystrons are thermally more favored than solid state shadowed by the Earth for up to 72 minutes per day)
(butterstick) to convert direct current (DC) electricity Solar arrays covert solar energy to electricity, which is
to radio-frequency (RF) energy at the transmitters in fed to microwave generators within the transmitting
these concepts. Using klystrons, the heat dissipation is antenna (transmitter) between the two solar arrays.
0.72 GW. Using solid state, the heat dissipation is 2.33 Then the transmitter transmits the energy to a
GW. The heat dissipation of the klystrons is 85% at receiving and rectifying antenna, known as "rectenna",
500°C, 10% at 300°C, and 5% at 125°C. All the heat on Earth, where the energy is reconverted into
dissipation of the solid state is at 100°C. Using electricity.
klystrons, the radiator area is 74,500 m2. Using solid As part of the SSP Exploratory Research and
state, the radiator area is 2,362,200 m2. Space Technology (SERT) program at the National
constructable heat pipe radiators are assumed in the Aeronautics and Space Administration (NASA), five
thermal analysis. Also, to make the SSP concepts system design concepts were evaluated in 1999 and
feasible, the mass of the heat transport system must be early 2000. They were:
minimized. The heat transport distance from the •Dual RF Reflector using klystron transmitter
transmitters to the radiators must be minimized. It can concept. 4
be accomplished by dividing the radiator into acluster •Dual RF Reflector using solid state (butterstick)
of small radiators, so that the heat transport distances transmitter concept?
between the klystrons and radiators can be minimized. •Single RF Reflector using klystron transmitter
The area of each small radiator is on the order of I m2. concept. 5
Two concepts for accommodating a cluster of small •Single RF Reflector using solid state (butterstick)
radiators are presented. If the distance between the transmitter concept)
transmitters and radiators is 1.5 m or less, constant •Integrated Symmetrical concept using klystron
conductance heat pipes (CCHPs) are acceptable for transmitter. 6.7
heat transport. If the distance exceeds 1.5 m, loop heat
pipes (LHPs) are needed. The mission life of the SSP concepts is 40 years.
Figure 1 shows the Dual RF Reflector concept. The
INTRODUCTION abacus structural frame provides runs for power
The concept of a Space Solar Power Station management and distribution (PMAD) cabling and
(SSPS) using a large photovoltaic solar array in permits a "plug and play" solar array approach for
geosynchronous (GEO) orbit around the Earth and assembly and maintenance. The concentrated solar
transmitting this power to Earth was first proposed by arrays always face the Sun with very little shadowing.
Glaser in 1968. I The SSPS in GEO orbit is stationary The solar concentrator uses shifting lens to
with respect to a desired location on Earth. The solar accommodate seasonal beta-tracking, and eliminates
array in geosynchronous orbit could receive up to 15 rotational joints between the cells and the abacus
flame. The reflector design eliminates massive rotary
joint and slip rings of the 1979 concept. The triangular
'AssociateFellow
'Copyright©2000TheAmericanInstituteofAeronauticsand truss structure provides a reasonable aspect ratio for
Astronautics,Inc.NocopyrightisassertedintheUnitedStates the abacus frame. The solar concentrators convert
underTitle17,U.S.Code.TheU.S.Governmenthasaroyalty- solar energy to electricity. The DC is converted to RF
freelicensetoexerciseallrightsunderthecopyrightclaimed
energy. Two transmitters transmit a total of 3.5 GW
herein forGovernmentalpurposes.Allotherrightsarereserved
bythecopyrightowner.
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of RF to a "rectenna" on Earth. The diameter of each The radiators sizes required are as follows:
transmitter is 500 m. • 33,400 m2at 500°C.
Figure 2 shows the single RF Reflector concept. • 13,000 m2at 300°C.
One transmitter transmits 3.5 GW of RF to a • 28,000 m2at 125°C.
"rectenna" on Earth. The diameter of the transmitter The total size of the radiators is 74,400 m2.
is 500 m. Concepts using Solid State (Butterstiek)
Figure 3 shows the year 1999 version of the In the solid state (butterstick) design concept,
Integrated Symmetrical concept. In this concept, 48 the efficiency of converting DC electricity to RE is
primary mirrors of 680-m diameter focus solar only 60%. Therefore, with a 3.5 GW RF output, the
radiation to two solar arrays. The total solar energy DC input is 5.83 GW, and the heat dissipation is 2.33
collected is 13.38 GW. The concentration ratio is GW. The temperature of the solid state electronics at
3.8:1. The solar arrays generate 4.41 GW of the transmitter is 100°C. The radiator area required is
electricity, which is converted to radio-frequency 2,362,200 m2, which is 6 times the total area of the
energy by klystrons on the transmitter. The diameter two transmitters.
of the each solar array is 1.55 km. The diameter of the Klystrons are more favored than solid state
transmitter is 1 km. In the year 2000 version (see because the radiator area is 32 times smaller. If both
Figure 4), there are 84 primary mirrors of 500-m sides of the radiator radiates heat to space, the radiator
diameter. The diameter of each solar array is 1.1 km. area is cut by half.
The diameter of the transmitter is 500 m.
The thermal analysis in this paper is meant to EFFECT OF HEAT TRANSPORT DISTANCE
show the order of magnitude type differences, and is BETWEEN RADIATORS AND TRANSMITTERS
not exact. The mass of the heat transport system from the
transmitters to the radiators in the SSP design concepts
RADIATOR SIZING FOR WASTE HEAT FROM has a very large impact on the feasibility of these
CONVERTING DC TO RF concepts. It is true no matter what heat rejection
Sizing of radiators in the SSP concepts using technology is used. The reason is that heat must be
klystrons and solid state (butterstick) are presented transported to an acceptable location before it can be
below. rejected to space. The heat rejection technologies
Concepts usin_ klystrons include space-constructable heat pipe radiator, rotating
Using high efficiency klystrons, the efficiency of film radiator, rotating solid radiator, liquid droplet
converting DC electricity to RF is 83%. Therefore, radiator, moving belt radiator, Curie Point radiator,
with a 3.5 GW RE output, the DC input is 4.22 GW, and variable surface area radiator. These advanced
and the heat dissipation is 0.72 GW. A breakdown of radiator technologies were proposed in the 1970s-
the heat dissipation of the klystrons at the transmitters 1980s. An assessment of these advanced radiator
is as follows: concepts was made by Juhasz and Peterson. 8
• 85% at 500°C. LHPs have high heat transport capacities. 9"1°'N
• 10% at 300°C. They can be used to transport the waste heat from the
• 5% at 125°C. transmitters to the radiators. The working fluids for
Due to the three very different temperatures, the LHPs in the SSP concepts using klystron
three different radiators are needed for each transmitters are assumed to be the following in the
transmitter. A space constructable heat pipe radiator _ thermal analysis:
is selected in this analysis because it is the most • Potassium at 500°C.
developed concept, and is a proven and reliable •Thermex at 300°C.
technology. The following assumptions are used in •Methanol at 125°C.
the thermal analysis of the radiators: The diameter of the LHPs is assumed to be 2.54
• One side of the radiators is on the anti-sun side and cm, and its wall thickness is assumed to be 0.09 cm.
The LHPs for 500°C and 300°C are made of stainless
radiates to space.
• In the GEO orbit, albedo and Earth infrared radiation steel. The LHPs at 125°C are made of aluminum.
are neglected. Each LHP has a single evaporator and transports 2 kW
• Emittance of the radiator, which has white paint as of heat from the transmitters to the radiators. Table 1
the coating, is 0.9. shows the distribution of the mass. The mass of the
• View factor of radiator to space is 1.0. heat transport system per unit RF output per unit
• The backside of the radiator is radiatively isolated distance between the transmitter and radiator is 262
from the SSP bus, which is at room temperature. metric tons/GW/m. A 33% redundancy is included.
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Figure
1. Dual RF Reflector Concept.
Nadir
Azimuth
Transmitter
Abacus
frame
Lightweight Fresnel
concentrator arrays J_":
Radiators
Ball-sc rew
activated links Orbit
Figure 2. Single RF Reflector Concept.
Arraysof
lightweight
Fresnel
Transmitter
Radiator
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Figure
3. Integrated Symmetrical Concept (1999 Version).
Primary
Mirrors
T
SolarArray 7.80km
dia1.55 km
Transmitter,
Radiator
4.9km
Figure 4. Integrated Symmetrical Concept (2000 Version).
Primary
Mirrors
Solar
Arrays
7.7km
Transmitter,
Radiator
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In the solid state (butterstick) concept, the locating the radiators at the rear face of the
working fluid for the LHPs is assumed to be ammonia, transmitters alone is insufficient to reduce the mass of
because the operating temperature of the electronics is the heat transport system to within budget. The
100°C. The diameter of the LHPs is assumed to be radiator must be divided into a cluster of small
2.54 cm, and its wall thickness is assumed to be 0.09 radiators, so that the heat transport distances between
cm. The LHPs are made of aluminum. Each LHP the klystrons and radiators are minimized. The area of
transports 2 kW of heat from the transmitters to the each small radiator is on the order of I m2.
radiators. Table 1 shows the distribution of the mass. Figure 5 presents the first concept for the
The mass of the heat transport system per unit RF location of a cluster of small radiators at the rear
output per unit distance between the transmitter and surface of the transmitters. All the radiators are 1.5 m
radiator is 340 metric tons/GW/m. A 33% redundancy from the transmitter. There is sufficient room for the
is included. DC distribution lines and solar array support structure,
The baseline RF output of the transmitters is 3.5 and for the robots to service the transmitters. The size
GW. In the dual RF reflector concept, the radiator of each radiator is approximately 1m x 1m. Only one
plane is perpendicular to the transmitter plane, and side of the radiators views space. The back of
there is a large radiator for each of the two transmitters radiators faces the transmitters. The heat transport
(see Figure 1). Also, the diameter of the transmitters distance is only 1% of the baseline.
is 500 m. To transport heat from some of the klystrons Figure 6 presents the second concept. The
across the transmitters to the radiators, the distance is minimum distance between the transmitter and
over 250 m. Suppose the average transport distance is radiators is taken to be I m, and the maximum
150 m, then the mass of the heat transport system is distance is taken to be 10 m. There is also sufficient
103,425 metric tons. It is larger than the mass of all room for the DC distribution lines and solar array
the other components combined in the SSP concept. support structure, and for the robots to service the
In the solid state (butterstick) concept, the mass of the transmitters. The height of the radiators is about 0.3 m,
heat wansport system is 139,400 metric tons. In the and the area is about 1m2.The radiators are located at
Integrated Symmetrical concept, the radiator is in the cylindrical envelopes. The diameter of the cylindrical
same plane as the transmitter. It has the same problem envelope closest to the transmitter is the largest. The
of heat transport distance as in the Dual RF Reflector diameter of the cylindrical envelope farthest from the
concept. transmitter is the smallest. With a special arrangement
To make the mass of the SSP design concepts of the radiators, not only the front of the radiators has
acceptable, the distance between the transmitters and a good view to space, but also the rear can view space
radiators must be minimized. at least partially. The average heat transport distance
is only 4% of the baseline.
PROPOSED RADIATOR CONCEPTS In both of these radiator configurations, each
As mentioned earlier, several advanced radiator radiator is integrated with a number of LHPs or
technologies were proposed in the 1970s-1980s. Space CCHPs to form a modular unit. The mission life is 40
constructable heat pipe radiator is selected in the years, and the design life of heat pipe radiators is
present thermal analysis because it is the most shorter. The modular heat pipe radiator units can be
developed concept, and is a proven and reliable replaced by robots in flight when needed.
technology. Recently, a lightweight carbon-carbon
composite prototype radiator was successfully THERMAL CONSIDERATIONS OF HEAT
fabricated and tested at NASA Glenn Research TRANSPORT METHOD
Center. _J The design operating temperature is 700 to Three methods of transporting heat from the
800 K. transmitters to the radiators are compared. They are
It was also mentioned earlier that for a 3.5 GW heat straps, LHPs, and CCHPs.
RF output, the total heat pipe radiator area required for
the SSP concepts using klystrons is 74,470 m2. In the Heat Straps
Dual RF Reflector concept, the radiator area required A thermal analysis of heat straps to transport
for each transmitter is 37,235 me, which is 19% of the heat from the transmitters to the radiators was
area of the 500-m diameter transmitter. The front face performed. The results are presented in Figures 7
of the transmitters transmits RF, and the heat through 9. Figure 7 shows the total cross-section area
dissipation of the klystrons is on the rear face. The of heat straps per unit length versus the temperature
klystrons are scattered on the transmitters. Therefore, gradient between the transmitter and radiator. A
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comparison of copper and composite material is also
made in Figure 7. The thermal conductivity of copper
is 3.91 W/cm-°C, and that of composite is 4.87 W/cm- Figure 6. Second Concept of Cluster of Small
°C. As the temperature gradient increases, the cross- Radiators.
section area decreases. For a 40°C gradient between
the transmitter and radiator, the total cross section area
of copper heat straps is 45,950 m2per meter length,
and that of composite is 36,800 mzper meter length. 1-1.5 m ,. Transmitter
Figure 8 shows the total mass of heat straps per
unit length versus the temperature gradient between
the transmitter and radiator. A comparison of copper I0
and composite material is also made in Figure 8. The
density of copper is 8.9 g/cm 3,and that of composite is
- A Number of Cylindrical Envelopes for Radiators, Largest
1.08 g/cm 3. For a 40°C gradient between the
Near Transmitter, and Smaller Away from Transmitter.
transmitter and radiator, the total mass of copper heat
straps is 412,198 metric tons per meter length, and that - A Number of Radiators on Surface of Each Cylindrical
of composite is 39,817 metric tons per meter length. Envelope.
Therefore, heat straps are not acceptable to transport
as much as 0.717 GW of waste heat from the
transmitters to the radiators because they are too
Figure 7. Cross Section Area of Heat Straps.
heavy.
Figure 9 shows the effect of the radiator 2OOOOO
temperature on the radiator area required for the 500°C AE 180000
klystrons, which contribute 85% of the total heat 180000
dissipation. The radiator area increases when the vu 14OOOO
o
radiator temperature decreases, that is, when the 120000
temperature gradient of the heat straps increases. If 100000 --Copper
.- Coml_slte
the temperature gradient between the transmitter and 8OOOO
radiator is neglected, the radiator area required for the 6OOOO
500°C klystrons is 37,615 m2. If the temperature 4OOOO
gradient is 40°C, the radiator area increases to 46,522 2OOOO
o
m2. The mass of the radiators increases when the
0
radiator area increases. This further makes heat straps
0 20 40 61) 80 100
unacceptable.
TemperatureGradient(*C)
Figure 5. First Concept of Cluster of Small Radiators.
Transmitter(500-mDiameter)Front
I
II
I
Figure 8. Mass of Heat Straps.
/ I-i.5 m
LHPsorCCHPs Radiator
Space
AllRadiatorsFaceSame Direction.
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Table 2 also presents the mass of the thermal
IM control system of the transmitters using CCHPs in the
dual RF reflector concept using klystrons. For a 3.5
GW RF output from the transmitters, if the distance
between the transmitter and radiators is 1m, the mass
,,_ 1200000
e_. 1000000 --Copper of the heat pipes is 1,423 metric tons per meter
-- Composite distance. The total mass of heat pipes is 1,423 metric
tons. If the heat transport distance increases, the heat
transport capacity of the CCHPs decreases, assuming
t 2ooooo
the outer diameter of the CCHPs to be 2.54 cm (1
0 inch). The product of the heat transport capacity and
0 20 40 60 80 100 transport distance is taken to be 1.37 kW-m. If the
distance between the transmitter and radiators is 5 m,
TemperaturGeradien(t°C)
the mass of the LHPs is 7,116 metric tons per meter
distance, and the total mass is 35,576 metric tons. A
33% redundancy is included.
Figure 9. Radiator Area vs. Radiator Temperature for
For CCHPs to be acceptable, the distance
500°C Klystrons.
between the transmitters and radiators is limited to
about 1 m to 1.5 m. The mass of the radiator
integrated with heat pipes is 575 metric tons. There is
no separate mass for the evaporators.
The differences between LHPs and CCHPs are
as follows. The wicks of LHPs are located at the
55000
evaporators, but the wicks of CCHPs are located along
5OOO0 the entire length of the heat pipes. The heat transport
capacity of LHPs is independent of the heat transport
distance, but that of CCHPs is strongly dependent on
40000
the heat transport distance. During startup, based on
the current technology, the entire length of the LHPs
needs to be heated by heaters, for example, to melt the
400 42O 44O 460 480 50O working fluid from solid to liquid. It would require
about 30 GJ of thermal energy, or 0.8 MW of heater
Radiator Temperature (*C)
power for ten hours, in the system shown in Table I.
The SSP needs to provide this heater power. The
LHPs versus CCHPs heater power is needed at startup only. The heaters
To reduce the mass of the thermal control can be kapton film heaters bonded to the exterior of
the LHPs. Heating at startup is not needed for CCHPs
system to an acceptable level, LHPs or CCHPs are
because there are wicks along the entire CCHPs.
needed. Basically, there is no temperature gradient
within the LHPs or CCHPs. There will be small Currently, the maximum operating temperature
temperature gradients at the interfaces due to contact in the heat pipe technology is under 200°C (water).
For LHPs to operate in the 300°C to 500°C range,
resistances. Table 2 below presents the mass of the
thermal control system of the transmitters using LHPs liquid metal is required. This high temperature LHP
technology has not been developed, but could
in the dual RF reflector concept using klystrons. For a
3.5 GW RF output from the transmitters, the mass of potentially be developed for SSP by 2020.
the LHPs is 676 metric tons per meter distance Liquid metal CCHP technology is an existing
between the transmitter and radiators. If the average technology. Liquid metal CCHPs were made and
distance is 5 m, then the mass of the LHPs is 3,378 operated successfully as early as 1973. Recently,
NASA Glenn Research Center has successfully
metric tons. A 33% redundancy is included. The
mass of the radiator and LHP condensers is 575 metric fabricated and tested carbon-carbon composite
tons, and that of the evaporator is about 500 metric prototype liquid potassium heat pipe radiators. _3
tons. It is assumed that the radiators are made of Liquid metal LHP technology is not an existing
carbon-carbon composite. A 1.0 view factor to space technology, mainly because there is no demand for it.
is assumed for all the radiators. Using the LHP technology and liquid metal heat pipe
7
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technologiyt,isfeasibleto
develop liquid metal LHP
technology.
Figures 10 and 11 present the mass and number 3_0_0
of CCHPs, respectively, versus the distance between
the transmitter and radiators. The product of heat 2_00
transport capacity and transport distance for the
_000_
CCHPs, which have a 2.54 cm (1 inch) outer diameter,
is taken to be 1.37 kW-m.
15_0_
The CCHPs or LHPs and radiator form an
integral unit. The radiator temperature is uniform. ._ 1000000
E
Although the radiators are small, while compared to a
5ooooo
single radiator of 30,000 m2or larger, they are still on
the order of 1 me. Using LHPs or CCHPs, the
temperature gradient between the transmitters and 0 1 2 3 4 5
radiators is much less than that of heat straps, and its
Distance (m)
effect on the size of the radiators is smaller.
SUMMARY AND CONCLUSIONS
The thermal control system required for the
Figure 10. Mass of CCHPs to Tansport 0.72 GW of solid state (butterstick) transmitter concept is much
Waste Heat vs. Distance Between Transmitter and larger and heavier than that required for the klystrons
Radiator (Redundancy Not Included). concept. The reasons are as follows. First, in the
klystrons concept, the efficiency of converting DC
electricity to RF is 83%. In the solid state concept, the
efficiency of converting DC to RF is only 60%.
Therefore, the heat dissipation in the solid state
concept is more than three times that in the klystrons
concept. Second, the klystrons operate at much higher
15OOO
temperatures. A breakdown of the heat dissipation at
1OOO0 the transmitters is as follows: 85% at 500°C, 10% at
300°C, and 5% at 125°C. The solid state electronics
50OO1 operate at about 100°C. Since space is the heat sink
for the waste heat, it is more effective to reject heat at
higher temperatures.
0 1 2 3 4 5
In the baseline Dual or Single RF Reflector
OImnce(m)
concept, and Integrated Symmetrical concept, there is
a large radiator for the transmitter. Also, the diameter
of the transmitter is 500 m. To transport heat from
Figure 11. Number of CCHPs to Tansport 0.717 GW
of Waste Heat vs. Distance Between Transmitter and some of the klystrons across the transmitters to the
Radiator (Redundancy Not Included). radiators, the distance is over 250 m. If the average
transport distance is 150 m, then the mass of the heat
transport system is 38,063 metric tons. It is larger than
the mass of all the other SSP components combined.
If solid state electronics are used, the mass is higher.
In order to make the mass of the SSP design concepts
acceptable, the distance between the transmitters and
radiators must be minimized. If LHPs are used, the
distance between the klystrons and radiators must be
on the order of several meters. Space constructable
heat pipe radiator is selected as the baseline because it
is the most developed concept, and is a proven and
reliable technology. The radiator area required for the
klystrons concept is 74,470 m2. Its mass is 355 metric
tons. In the Dual RF Reflector design concept, the
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radiator area required for each transmitter is 37,235 6. Perkinson, D., et al., Integrated Symmetrical
m2, which is 190 of that of the transmitter. In the Concept, Marshall Space Flight Center,
Single RF Reflector concept and Integrated Huntsville, AL, Nov. 1999.
Symmetrical concept, there is only one transmitter, 7. Perkinson, D., e_ al., Integrated Symmetrical
and the radiator area is 38% of that of the transmitter. Concept, Marshall Space Flight Center,
The radiator area required for the solid state concept is Huntsville, AL, Feb. 2000.
2,362,162 m2. It is twelve times the area of that of a 8. Juhasz A. J. and Peterson, G. P., Review of
transmitter. Its mass is 9,921 metric tons, which is Advanced Radiator Technologies for Spacecraft
30% to 40% of the total mass budget for the SSP. For Power Systems and Space Thermal Control,
these reasons, the SSP concepts using klystrons are NASA Technical Memorandum 4555, June 1994.
favored thermally. The concepts of using solid state 9. Ku, J., Operating Characteristics of LHPs, SAE
are not practical. Technical Paper Series 1999-01-2007.
The klystrons are scattered on the transmitters. 10. Kaya, T. and Ku, J., A Parametric Study of
Therefore, locating the radiators at the rear face of the Performance Characteristics of LHPs, SAE
transmitters alone is insufficient to reduce the mass of Technical Paper Series 1999-01-2006.
the heat transport system to within budget. The 11. Kaya, T. and Ku, J., Ground Testing of LHPs for
radiator must be divided into a cluster of small Spacecraft Thermal Control, AIAA Paper 99-
radiators, so that the heat transport distances between 3447.
the klystrons and radiators are minimized. The area of 12. Dunn, P. and Reay, D. A., Heat Pipes, Third Ed.,
each small radiator is on the order of 1 mz. The Pergamon Press, 1982.
envelope of the radiators is about 1.5 m from the 13. Juhasz, A. J., Design Considerations for
transmitter. Another configuration of accommodating Lightweight Space Radiators Based on Fabrication
a cluster of small radiators is to locate them at and Test Experience with a Carbon-Carbon
cylindrical envelopes behind the transmitter. The Composite Prototype Heat Pipe, NASA/TP-1998-
diameter of the cylindrical envelope closest to the 207427, Oct. 1998.
transmitter is the largest, and that of the cylindrical
envelope farthest from the transmitter is the smallest.
With a special arrangement of the radiators, not only
the front of the radiators has agood view to space, but
also the rear can view space at least partially. The
minimum distance between the transmitter and
radiators is 1 m, and the maximum distance is 10 m.
The height of the radiators is about 0.3 m, and the area
is about 1m2.If the distance between the transmitters
and radiators is 1.5 m or less, CCHPs are acceptable
for heat transport. Ifthe distance exceeds 1.5 m, LHPs
are needed.
REFERENCES
1. Glaser, P. E., "Power from the Sun: Its
Future," Science, Vol. 162, Nov. 1968, pp.857-
886.
2. Williams, J. R., "Geosynchronous Satellite Solar
Power," Astronautics and Aeronautics, Dec. 1975,
pp. 46-49.
3. Glaser, P. E., "Evolution of the Satellite Solar
Power Station (SSPS) Concept," J. of Spacecraft,
Vol. 13, Sep. 1976, pp. 573-576.
4. Carrington, C., et ai., Dual RF Reflector Abacus
Concept, Marshall Space Flight Center,
Huntsville, AL, Oct. 1999.
5. Carrington, C., et al., Single RF Reflector Abacus
Concept, Marshall Space Flight Center,
Huntsville, AL, Nov. 1999.
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American Institute of Aeronautics and Astronautics
Table 1. Thermal Control Systems in SSP Concepts using Klystrons versus Solid State.
Klystrons Solid State
(Butterstick)
RF Output from Transmitters (GW) 3.5 3.5
Efficiency of Converting DC to RF (%) 83 60
DC Input (GW) 4.2169 5.8333
Waste Heat (GW) 0.7169 2.3333
Ratio of Waste Heat to RF Output (GW/GW) 0.2048 0.6667
Distribution of Waste Heat 85% at 500°C; 10% at 100% at -100°C
300°C; 5% at 125°C
Size of Radiator (m2) 74,470 2,362,162
Mass of Radiator (Metric Tons) @ 4.2 kg/m: i97.2 9,921
Mass of Radiator Per Unit RF Output (Metric Tons/GW) 164.3 2,835
Number ofLHPs @ 2 kW per Loop with 33% Redundancy 169,440 1,551,800
Material of Piping Stainless Steel 300°C & Aluminum
500°C; Aluminum 125°C
Working Fluid Potassium 500°C; Ammonia
Thermex 300°C;
Methanol 125°C
LHP Technology Liquid Metal Not Current Current
Distance Between Transmitters and Radiators (m) 100 100
Mass ofLHPs @ 2 kW per Loop with 33% Redundancy 68,840 89,300
(Metric Tons)
Mass of LHPs Per Unit Distance Between Transmitters and 688 893
Radiators (Metric Tons/m)
Mass of LHPs Per Unit RF Output (Metric Tons/GW) 19,657 25,510
Mass of LHPs Per RF Output Per Unit Distance Between 197 255
Transmitters and Radiators (Metric Tons/GW/m)
Mass of LHP Evaporator Per RF Output Per Unit Distance -500 ~280
Between Transmitters and Radiators (Metric Tons/GW/m)
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